The present invention concerns a passenger vehicle tire whose outer surfaces are of different colors and, in particular, a tire presenting a color other than black on the sidewalls and at least one color other than black on the tread.
With the advent of rubber compounds containing silica as principal filler instead of carbon black, it is possible to make white and/or color compounds, other than black or white, by addition of coloring pigments. A compound of color other than black can be used as a single component of the tread, or in combination with a standard black compound and/or another color compound. In case of combination on a tread of compounds of different colors, and with a view to making the wear of said tread uniform, while maintaining a high level of wear potential, the chemical composition of the different rubber compounds should be studied accordingly.
The combination of several compounds of different compositions on the same tread is well known. Patent Application FR 2,611,600, in order to reduce the irregular wear of an airplane tire tread, without detriment to the need to strengthen the underlying reinforcement, proposes dividing said tread axially into three parts: two lateral parts, the constituent rubber compound of which has a modulus at 100xc2x0 and at 100% elongation 30 to 80% lower than the modulus measured under the same conditions as the rubber compound constituting the central part.
Said combination can, in case said compounds are of different colors and said compounds are structurally arranged in any way, entail major problems with the lifetime of the radial tire, the latter containing a crown reinforcement made up of at least two crown plies of inextensible and crossed reinforcing elements radially surmounting a radial carcass reinforcement. In particular, complex phenomena of migration between compounds of certain constituent additives can harmfully influence endurance in separations between ends of said xe2x80x9ccrossedxe2x80x9d crown plies of the radial tire, and/or separations between crown reinforcement and carcass reinforcement over a long lifetime of use of the tire.
In order to remedy said problems, the tire according to the invention, having a radial carcass reinforcement, a crown reinforcement composed of at least two crown plies of inextensible reinforcing elements, preferably wire, parallel to each other in each ply and crossed from one ply to the next by forming an angle with the circumferential direction that can range between 5xc2x0 and 45xc2x0 and radially outside a tread, composed of rubber compounds of different colors, and axially formed by at least three longitudinal parts, is characterized in that the two lateral parts of the tread, radially covering the axial ends of the crown plies whose reinforcing elements are crossed from one ply to the next by forming an angle with the circumferential direction that can range between 5xc2x0 and 45xc2x0, consist of a rubber compound of a first color, axially between the said two parts, at least one part consisting of a rubber compound of a second color, different from the first and other than black, each axial end Axe2x80x94visible outside the tirexe2x80x94of the colored part with a second color being away from the endxe2x80x94situated on the same side relative to the equatorial plane of the tirexe2x80x94of the axially narrowest crown ply by a distance at least equal to 30 mm.
The best compromise between uniformity of wear and crown reinforcement endurance is obtained when the two lateral parts of the tread are black.
Between the two lateral parts there can be a single central part of a rubber compound of a second color, or also a central part axially connected to the two lateral parts of the first color by means of two intermediate parts, the colored part of the tread with a second color that can then be either one intermediate part or two intermediate parts, and the central part that can be of a first color, or of a color different from the second color of the intermediate parts.
The radial thickness of the compound of color other than black can have a value ranging between the total thickness of the tread, measured in the equatorial plane, and a value equal to the radial distance separating the tread surface from the radially outer surface of the wear indicators, placed at the bottom of the grooves. Said thickness, for reasons of ease and cost of manufacture, is advantageously equal to the thickness of the tread.
Improvement of the endurance of the crown reinforcement of such a tire can be completed by the presence, radially above the crown plies, of reinforcing elements crossed by at least one additional ply of circumferential reinforcing elements, the axial width of which ply is greater than the width of the widest xe2x80x9ccrossedxe2x80x9d crown ply and said additional ply fulfilling two functions: a hooping function, as known, but also a migration screening function of the compounding additives and, in particular, of the antiaging additives, owing to its proper thickness and the composition of its liner.
It is particularly advantageous to use two plies of circumferential reinforcing elements for the above purposes, preferably of aliphatic polyamide, the two plies having widths greater than the width of the widest xe2x80x9ccrossedxe2x80x9d crown ply. For maximum efficiency, the ply of axially narrowest circumferential elements will have a width equal to at least 105% of the width of the widest xe2x80x9ccrossedxe2x80x9d crown ply, the latter being greater than the width of the contact surface between the road and the tread of the tire, inflated to working pressure and carrying its nominal load.
In order to have, on the one hand, a tread wear as regular as possible crosswise, in spite of the presence of at least two compounds of different composition and color, and, on the other, to minimize the risks of separation between products on the tread surface, the ends Axe2x80x94visible outside the tirexe2x80x94of the two axial edges of each part of second color will be located at the bottoms of circumferential grooves, axially delimiting said part of second color, said circumferential grooves preferably being longitudinal.
The color tire, according to the invention, has at least one of the sidewalls, at least partially, in a color other than black, with an arrangement of rubber compounds known per se, the color compounds axially outside being radially delimited by two sidewall protuberances axially projecting outside. The curvilinear distance separating the radially upper end of the colored sidewall compound from the axially outer end of the widest xe2x80x9ccrossedxe2x80x9d crown ply is advantageously at least equal to 30 mm.